The present invention relates generally to brush seals and particularly relates to arcuate brush seal segments resiliently mounted between a rotating component and a component fixed against rotation.
Brush seals are commonly used to seal the gaps between a rotating component and a stationary component. For example, in turbomachinery, brush seals are commonly used to seal between a rotating shaft, i.e., a rotor, and a fixed housing or stationary component about the rotor.
Typically, the brush seals are provided in arcuate segments, generally corresponding to the circumference of the components to be sealed. Each segment includes mounting plates between which brush bristles are disposed. The bristles have free ends projecting radially beyond the edges of the mounting plates for engagement against, and forming a seal with, the rotating component. To maintain the bristles between the mounting plates, the arcuate radial outer face of the mounting plates and the bristles exposed at their ends in the space between the mounting plates are welded to one another.
In a typical installation, one of the mounting plates includes an axially extending flange or hook. The annular radially inwardly opening groove of the stationary component in which the brush seal segment is disposed also includes a slot opening axially into the groove. The groove and slot are sized such that the brush seal segment is movable axially in one direction under higher pressure forces on one side of the segment than on the opposite side, i.e., higher pressure on the upstream side than on the downstream side, to maintain the downstream mounting plate against an end wall of the groove. The annular space between the outer face of the brush seal segment and the base of the arcuate groove, in operation of the turbomachinery, presumably has a pressure equal to the upstream pressure. This pressure maintains the arcuate seal segment biased in a radial inward direction to engage the inner surface of the hook against the outer surface of the flange of the stationary component. These pressure forces work well when the seal is assembled in the upper half of the stationary component of a turbine where gravity acts in a downward direction. This affords a natural engagement of those surfaces with one another and a radially inward positioning of the brush seal segment relative to the stationary component groove.
However, for brush seal segments in the lower half of the turbine casing, it will be appreciated that the radially inwardly facing surfaces of the segment hooks are spaced from the radially outwardly facing surface of the stationary component flange since the gravitational forces locate the brush seal segments in their radially outermost position. At turbine startup, the higher pressure biases the brush seal segments in a downstream axial direction. However, because there is no gap between the brush seal segments and the base of the groove, the brush seal segments are not displaced radially inwardly to engage the bristles against the rotor, thus leaving significant leakage gaps between the stationary and rotating components rendering the brush seal is ineffective.
Efforts to alleviate this problem have included the use of set screws through packing rings to align the seal with the appropriate mating surfaces upon assembly of the seal into the turbomachinery. Another effort to alleviate the problem is described and illustrated in U.S. Pat. No. 6,331,006, of common assignee herewith. These methods, however, are not applicable to all brush seal installations. In addition, the leaf spring disclosed in U.S. Pat. No. 6,331,006 cannot be readily installed at great distances from the ends of the diaphragm halves of the turbomachinery. Insertion of the brush seal segments and leaf springs disclosed in that patent at locations remote from the insertion entry location is difficult.
In accordance with a preferred embodiment of the present invention, there is provided a brush seal segment in combination with a leaf spring attached to the outer surface of the segment. One end of the leaf spring is secured, preferably by welding, adjacent an end of the brush seal segment. The leaf spring includes a pair of reversely curved portions, i.e., first and second curved portions, for contact with the stationary component and brush seal segment, respectively. The first curved section extends from the end secured to the segment radially outwardly until at a location intermediate opposite ends of the leaf spring, the spring engages the base of the groove of the stationary component. The second curved portion engages the outer face of the brush seal segment and has an upturned end. The second curved portion enables the spring to flatten out and return by way of the relative movement of the second curved portion along the outer face of the brush seal segment as the spring is loaded and unloaded.
Because the brush seal segment and spring are secured to one another, e.g., by welding, they constitute essentially a unitary integral part having the capability of sliding in a circumferential direction in the groove of the stationary component to an appropriate location for the brush seal segment. Positive engagement between the curved portions of the spring and the stationary and rotating components upon insertion is maintained because of the natural curvature of the leaf spring. Also, absent a positive force causing the seal to slide along the circumferential groove, the seal will remain fixed, serving as an anti-rotation feature for assembly and during operation.
In a preferred embodiment of the present invention there is provided a brush seal and spring combination for disposition between a first rotatable component and a second component fixed against rotation, comprising an arcuate brush seal segment for disposition between the first component and the second component and including a pair of arcuate plates and a plurality of brush bristles projecting therefrom having free ends for sealing with the first rotatable component, and an elongated leaf spring for disposition between the brush seal segment and the second component, the leaf spring being secured adjacent one end to the brush seal segment and having first and second circumferentially extending reversely curved portions, the first curved portion projecting away from the brush seal segment for engaging the second component at a location along the spring intermediate opposite ends thereof, the second curved portion being located adjacent a second end of the spring opposite the one end and in engagement with the brush seal segment.
In a further preferred embodiment of the present invention there is provided a brush seal assembly, comprising a first rotatable component having an axis of rotation; a second component fixed against rotation about the axis and radially outwardly of the rotatable component, the fixed component having a radially inwardly opening groove and an axially opening slot in communication with the groove; an arcuate brush seal between the rotatable component and the fixed component in the groove and including an axially projecting hook for reception in the slot, the brush seal having a support mounting a plurality of bristles projecting therefrom and having free ends in sealing relation with the rotary component, the support having an arcuate radial outer surface, a leaf spring between the fixed component and the outer face for biasing the brush seal for movement in a generally radially inward direction, the leaf segment being secured adjacent one end to the brush seal adjacent one end of the spring and having first and second reversely curved portions, the first curved portion projecting away from the brush seal for engaging the second component at a location along the spring intermediate opposite ends thereof, the second curved portion being located adjacent a second end of the spring opposite the one end and in engagement with the brush seal outer face.